October 1992

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Any projection into the future of ophthalmic laser surgery must recognize the long history underlying the ophthalmic experience with lasers. By comparison, other medical applications are "Johnny-come-latelies" to laser use. For many years, retinal photocoagulation was the only widespread laser application in surgery and medicine. This early application was based on clinical experience starting in 1954 with non-laser (i.e., xenon arc) retinal photocoagulators. In spite of their bulk and clumsy application interface, they provided a body of clinical experience that prepared the eye surgeon for the advent of laser technology.

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Investigators have been evaluating the possibility of using laser energy to treat obstructive arterial disease for over a decade. The primary goals of these endeavors have been to address some of the limitations of conventional balloon angioplasty, such as recanalization of chronic total occlusions refractory to guidewire passage and reduction of restenosis rates.

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Lasers have not been universally accepted in orthopedic surgery. In fact, there is a strong resistance to the development of this technology. However, it seems that there may be a significant place for lasers in the treatment of musculoskeletal lesions and that wide acceptance of lasers in orthopedic surgery will depend on the facilitation of operations and techniques currently dependent on mechanical instrumentation, as well as making the procedures cost-effective. During the past five years, orthopedic surgeons have found many applications for lasers. These include laser applications in arthroscopy, discectomy, joint revisions, and tissue welding.

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During the past decade, lasers have had a dramatic positive impact on the treatment of diseases in women. The precise application of intense light energy of varying wavelengths may be clinically used to safely destroy only diseased tissue areas, while maximizing preservation of the normal reproductive tract. The result is often less scarring and post-operative pain during a shortened recuperative time.

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By now, the fundamentals of photodynamic therapy (PDT) are well known. A photosensitizer is injected intravenously into a patient who has a solid tumor of known location and, following localization of the sensitizer into the lesion, local photoactivation by an appropriate light source is carried out. Assuming that an effective combination of drug and light are used, the tumor can be reduced or, in many cases, completely eradicated, depending on size and location.

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The precision and power of lasers has led to a spectrum of different applications in both physical and biomedical sciences. However, surgical uses have been limited to "external" thermal effects, including cutting, cauterizing, and welding of tissues by the intense energy within the narrow laser beam. A largely unexploited and potentially unlimited new approach is to use lasers as a source of monochromatic energy for interstitial tissue destruction of benign and potentially malignant diseases of the head and neck, brain, breast, liver, spine, and prostate via a minimally invasive technique such as "one needle stick."

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General surgery has seen the most rapid increase in laser utilization over the last several years, with many more procedures being carried out with the laser as the surgical tool, replacing the knife and electrocautery.1 Although the carbon dioxide laser was initially used, the contact Nd:YAG has significantly expanded the use of lasers in the traditional areas of incision, excision, vaporization, and coagulation. Other laser wavelengths include the KTP and holmium.

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Near-infrared spectroscopy (NIRS) is an emerging technique for continuous, noninvasive bedside monitoring of tissue structure, oxygenation, and blood flow. It relies upon the relationships that variations in the concentration of light-absorbing oxygen-carrying pigments produce proportional changes in the way these proteins absorb light, and that variations in concentration and tissue structure affect the path of light through tissue.

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Optical tissue diagnosis through the experienced doctor's eye has long been a prime method in medical examinations. Through the development of endoscopic techniques, it has also become possible to gain optical access to many inner organs, such as the lungs, urinary bladder, gastrointestinal tract, and larger vessels. Through the biopsy channel of such fiber optic instruments, it is also possible to collect specimens for histopathological investigation and to perform treatment procedures such as employing laser radiation. An extension of the optical diagnosis using reflected light is provided by the fluorescence phenomenon.

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It is often imperative in the treatment and management of critically ill patients to know the pH of the blood plasma and the concentration of oxygen and carbon dioxide in the blood. These analytes are collectively referred to as the "blood gases." The conventional method for determining blood gas values involves drawing a sample of blood from the patient, transporting it to a centralized laboratory, and using an electrochemical blood gas analyzer to measure its pH, oxygen partial pressure (P02), and carbon dioxide partial pressure (PC02).

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Recent years have seen the medical field in a growing state of critical controversy and discussion over escalating costs and how best to control them. Medical reimbursements from government and insurers to doctors and hospitals have been significantly cut for many procedures. Hospitals are required to look more closely at costs and how to make their equipment purchases more useable for multiple doctors and procedures. Noninvasive surgical procedures are becoming more desirable in the medical regimen. Thus, demands on device manufacturers in the implementation of new equipment capability are broad.

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The application of flow cytometric (FCM) instruments for automated analysis and separation of cells and organelles has provided new dimensions to biomedical research and clinical medicine by making it possible to analyze and isolate cells and organelles, e.g., chromosomes, with particular physical, biochemical, and immunological properties. This technology represents an exciting departure from conventional microscope-based cytophotometric procedures that require up to several hours to measure and process several hundred cells. In FCM systems, the uniqueness is that multiple measurements are made on a cell-by-cell basis at rates up to 3 X 105/min., statistical precision is high, and subpopulations are detected and separated from heterogeneous mixtures for identification and/or for functional and biochemical analyses.

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Diffractive optics is a well established field in the optical sciences. And yet, there has been a significant increase of interest in diffractive optics over the last couple of years. This is largely due to the adaptation of VLSI manufacturing techniques, such as photolithography and dry etching techniques used to fabricate the optical elements. The use of these techniques allows one to generate high quality elements that can be engineered for a variety of applications with more flexibility than it is possible with conventional fabrication techniques. To describe this new field of diffractive optics which deals with components generated by computer and lithographic fabrication, the term "binary optics" is often used.

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In developing one of the "Light Touch" articles a few months ago, my daughter and I were observing various optical effects while shining a flashlight around in a dark room. One of the most surprising to her was the way a shiny object looks. Whereas we could see the shape of the flashlight beam on the wall, we could only see glints on a shiny object such as a door knob: the rest of the door knob appeared dark. When I asked her what parts of the door knob were bright, she thought at first that it was the portions of the object that were closest. Then she realized it was the portions of the object that were facing us; she said that it acted like a mirror.

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I'm often asked: "What is NAPM and what do they have to do with optical standards?" NAPM—the National Association of Photographic Manufacturers—is an industrial trade association of manufacturers that make products related to photography and imaging technology. One of NAPM's original functions was to act as the administrative body for the domestic and international writing of standards related to photography and the various commercial products used in photography. In this role, NAPM served as the ANSI administrative secretariat for the ANSI PH Committee for photography and as the ISO Secretariat for ISO/TC42 Photography.

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